(i) Technical Field
The present invention relates to a developing device and an image forming apparatus using the same.
(ii) Related Art
In an image forming apparatus, such as a copying machine or a printer, an electrostatic latent image formed on a surface of a photoconductor drum is developed into a toner image by causing toner supplied from a developing device, which is set so as to oppose the surface of the photoconductor drum, to adhere to the electrostatic latent image.
In such a developing device that performs development, since toner density is reduced due to consumption of the toner by the development, if any developer remaining on a developing roller without being used for the development is repeatedly transported as it is to a development area, it is not possible to perform proper development, as a result of which image failure occurs. Therefore, it is necessary to separate the developer remaining on the developing roller from the developing roller and return the separated developer to a developer supply mechanism that is set in the developing device.
In order to achieve a high-speed image forming apparatus, a double developing device including double developing rollers for reliably performing development is available as a developing device. In the double developing device, any residual developer remaining on the lower developing roller without being used in the development is collected by a developer supply mechanism as a result of being separated from the lower developing roller when magnetic restraining force is lost at a separating pole. Even if the residual developer remains on the surface of the developing roller because the developer is not completely separated, a large amount of developer prior to the regulation of a layer and newly supplied from the developer supply mechanism is mixed with the residual developer. Therefore, the influence on a reduction in toner density at the lower developing roller is relatively small.